rp 937 
.H3 

Copy 1 


How toProtict 
Structural 
Metal 








* 
























T' . 












































- • 

■f ' 

- 

v 

** 

' 








' 




. 

























937 

3 

»py 1 








How to Protect 
Structural 
Metal 


A Practical Hand Book Upon the Mixing and 
Application of Paint to Iron or Steel, Tin, 
and Galvanized Iron, Together with 
a Brief Explanatory Discussion 
of the Causes of Corrosion 
and Remedies for It 



NATIONAL LEAD CO. 


NEW YORK, BOSTON, BUFFALO, CHICAGO, CINCINNATI, CLEVELAND, 
ST. LOUIS, (JOHN T. LEWIS & BROS. CO., Philadelphia) 
(NATIONAL LEAD & OIL CO.. PITTSBURGH) 



Copyright, 1909 
By O. C Hark 



© / 2 -, C 1 
Cla. fl, 243889 

JUl - 14 ,'909 






Difference in Paints 


M isunderstanding of what paint is, what it 

can be reasonably expected to accomplish, and how 
it performs its duty in preserving and beautifying objects, 
is responsible for a great loss of money, both to the small 
property-owner and the great manufacturer. 

To the average person paint is paint, and the first 
error to which this lack of discrimination leads is the 
use of the same paint for all purposes and under all 
conditions. 

That pure white lead and pure linseed oil, mixed 
properly to suit the special conditions under which the 
paint is to be used, is the best possible protection for 
wood, brick and cement, cannot be gainsaid. But when 
it comes to the painting of a metal surface, white lead, 
though good, must yield first place to red lead. 

To show fully just why this is so would require a long 
explanation of what corrosion is, a comparison of pro¬ 
posed methods to stop or retard it and an intricate 
examination of the chemical and physical properties of 
various materials. This would be out of place in a 
practical hand-book designed for the daily use of the 
architect, engineer and painter, such as this little book¬ 
let aims to be. 

Enough of the theoretical phase of painting metal 
surfaces must be given, nevertheless, to satisfy the 
intelligent inquirer that the methods recommended are 
scientific. 


Tendency of Metals to Corrode 

The relative tendency of various metals to corrode or 
oxidize is shown by the following table; those which 
corrode most easily b$ing placed, first and those which 


6 How to Protect Structural Metal 

resist corrosion more successfully following in their 
order. Zinc, the most easily corroded, is thus at the top, 
and gold, the most resistant, at the bottom of the list. 
Zinc 

Aluminum 

Cadmium 

Iron 

Steel 

Nickel 

Lead 

Hydrogen 

Copper 

Mercury 

Silver 

Platinum 

Gold 

In practical affairs iron, in one form or another, is 
the metal principally used. By the above list it will 
be seen that iron is one of the most readily corroded. 
Our attention will be given entirely, therefore, to this 
metal, either bare or covered with a coating of tin or 
zinc. 


Decay, Both Internal and External 

Iron and steel, then, are subject to decay. That is 
to say, they are liable, under certain conditions, to 
lose some valuable quality which weakens them. If 
this loss is internal it may be caused by what is called 
“fatigue” due to crystallization or to loss of strength 
through strain. The crystallization cannot be pre¬ 
vented by painting. If the decay is external it is due 
to oxidation of the surface, i. e. the metal rusts. This 
can be prevented by proper painting. 

Iron and steel will not rust at ordinary temperatures 
except in the presence of moisture; therefore, contact 
of water or moist air with the metal is the thing to 
be feared and, if possible, prevented. Water and air 
are known as the primary causes of corrosion. To 
these must be added a number of secondary causes or 


How to Protect Structural Metal 


7 


accelerators of corrosion, such as, first, rust itself, 
because it absorbs and holds moisture to the surface; 
second, carbonic and other acids; third, neutral or acid 
salts in solution; fourth, roughness in the surface; fifth, 
foreign matter, such as scale, on the surface; sixth, 
inequalities in surface conditions due to imperfectly 
made metal; seventh, stray electric currents. 

Methods of Preventing Rust 

Rusting is a galvanic or electric action and the ill 
effect of all these secondary causes or accelerators of 
corrosion is due, in the final analysis, to electric action 
which they set up in the iron or steel. If we could stop 
the electric action produced in iron under certain con¬ 
ditions, there would be no corrosion and iron would 
become a noble metal. This can be done temporarily 
by immersing the iron in an alkali solution; but as soon 
as the iron is taken out, it rusts as before. The alka¬ 
line-solution method of preserving iron is therefore 
impracticable for most purposes. To use alkalies in 
paints is not practical because they decompose the oil 
and are soluble in water. 

Another method by which the galvanic action can be 
prevented is to treat the iron with solutions of chromic 
acid or certain forms of concentrated nitric acid. But this 
treatment, also, at the present state of practice, is found 
to be of but temporary value, for the iron gradually 
returns to its original state, in which it rapidly corrodes. 

Both the above methods attempt to change the 
nature of the iron itself and render it immune to gal¬ 
vanic action. They are interesting and some day a 
method may be found to render permanently effective 
the change which they undoubtedly make in the iron 
itself. But until that day comes we are compelled to 
leave the nature of the iron as it is and protect it from 
the causes which set up the electric action within it. 
In other words, we have to paint it. And the paint 
must be made of some material which will not itself 
start galvanic action by contact with iron and which 


8 How to Protect Structural Metal 

will effectually keep out water or other injurious elements. 
There are several candidates for selection as protectors 
of metals from corrosion. Before examining them spe¬ 
cifically, let us observe what the requisites of a good 
paint for iron and steel are. 

What Constitutes a Good Paint 

Asking this question regarding preservative coatings 
for iron and steel, we find it necessary to point out that 
a paint which may be a good paint for the under coats 
may prove to be an undesirable paint for the outer or 
finishing coats, and vice versa. We will call the paint 
which is to go next to the metal the “protective paint,” 
and the paint which comes outside, the “finishing 
paiqt.” The finishing paint should be, in reality, a 
“protective paint” also, but, for clearness in discussion, 
it is necessary we should make a distinction. 

The protective paint should measure up to the fol¬ 
lowing 


General Qualifications: 

First —It should form a hard, adherent foundation 
for subsequent coats. There is nothing else which tends 
so much to the cracking, checking and alligatoring of 
paint as the application of relatively hard coats over 
relatively soft coats. This is an observation which 
should be kept in mind not only in the painting of metals 
but in all painting. That the priming coat should have 
the power to adhere tenaciously to the surface is self- 
evident. 

Second —The pigment constituents of a protective 
paint should be inhibitive of corrosion. This means 
that it should tend to give passivity to the particles of 
the iron itself—should by its nature tend to prevent 
that activity of molecules which we have described 
as galvanic and which causes corrosion. 

Third —A protective paint should be a non-conductor 
of electricity. The corrosion of iron and steel being 
the result of a galvanic action, it is necessary not only 


How to Protect Structural Metal 


9 


to put on a paint which will be inhibitive, that is, keep 
out those influences which will set up the galvanic action 
in the iron itself, but it is supremely necessary also to 
bar the way to stray electric currents from the outside. 
In these days when electrically charged wires run every¬ 
where, under the streets, overhead and through all 
buildings, the leakage of electric currents is an every day 
problem. The real solution of the problem would seem 
to be to confine these electric currents where they belong 
instead of allowing them to run riot among neighboring 
property. Motives of economy itself will doubtless 
some day lead the owners of the runaway electricity to 
correct this evil themselves, but until that day arrives, 
we must do our best to protect our property against 
currents which are running amuck. 

Some pigments are good conductors of electricity. 
These should be avoided in paint intended for the pro¬ 
tection of iron and steel. 

Fourth —A protective paint should contain no com¬ 
pounds soluble in water. The reason for this is appar¬ 
ent. If any of its constituents is soluble in water, which 
is one of the chief enemies we are fighting, the paint 
will soon go to pieces under service conditions. Water- 
soluble compounds may also, under certain conditions, 
unite with other elements to form new compounds 
favorable to the conducting of electricity. 

Fifth —A protective paint should be as impermeable 
as possible. This qualification scarcely needs comment. 
One prime purpose of a protective paint is to keep out 
water. If it is porous, moisture—a principal cause of 
the galvanic action which causes rust—will find easy 
entrance. 

Sixth —Protective paint should vary in color in its 
different coats. This is one of the most important 
requisites of a protective paint, but one which is very 
often overlooked or ignored. Poor workmanship is 
responsible in very great part for the failure of protec¬ 
tive coatings. Paint is often applied by cheap and 
inefficient labor, and if each successive coat of paint is 
of the same color as the preceding one, it is impossible 


10 


How to Protect Structural Metal 


for an inspector to detect slighted parts.. Above all, 
the first coat should be very different in color from the 
natural color of the metal and the finishing coatings 
should be different from the protective coats. 

Available Paints 

There are several materials in more or less general use 
as protective paints for metals. A brief examination of 
the nature of these materials will enable us to see how 
they measure up to the standard set by the foregoing 
requirements. 

Linseed Oil. —Linseed Oil, without a pigment, is 
sometimes recommended as a priming coat for iron or 
steel, but such a practice cannot be too emphatically 
condemned. Linseed oil is the best vehicle to use with a 
good pigment, but when used alone it fails to meet four 
of the important requirements given. 

In the first place, linseed oil forms a film which always 
remains soft as compared with later coats containing 
pigments. The cracking and alligatoring of the sub¬ 
sequent paint is almost inevitable. 

In the second place, linseed oil is not an inhibitor of 
corrosion, and it separates the iron and steel from the 
subsequent paints, thus nullifying any rust-inhibiting 
power which the later coats possess. 

In the third place, it is more or less porous and, the 
film being thin, it is permeable. 

In the fourth place, linseed oil is transparent, making 
it almost impossible for an inspector to tell whether or 
not the surface has been perfectly protected by it. 

Mineral Oils. —No mineral oil or non-drying oil of 
any kind should be used in a protective coating. They 
prevent the paint from becoming sufficiently hard to 
give a good foundation for subsequent paint. Linseed 
oil, when used alone as we have seen above, makes a soft 
film, but when used with a pigment, especially if a part 
of the oil is boiled, the film will dry hard. Linseed oil, 
therefore, should be used with a pigment in all protec¬ 
tive coatings. 


How to Protect Structural Metal 


11 


Asphaltum. —The objection to asphaltum, which is 
sometimes used, is that it tends to work through all 
subsequent coats and never becomes sufficiently hard 
to give a good foundation for the later films. It thus 
violates requirement No. 1. 

Graphite and Carbon. —These substances do not 
possess inhibitive qualities, and they also give to a 
protective coating the power to conduct electricity. 
They therefore violate two of the most important laws 
laid down for protective paints. Carbon also absorbs 
so much oil as to make it a mere wash. A paint in which 
the pigment forms only one part and the oil four parts 
is undoubtedly easy to spread but there cannot be much 
protection in the film. Finally, the similarity of color 
between the black graphite or carbon and the dark 
iron makes it difficult to detect imperfections in the 
application of such a paint. 

Iron Oxides. —The oxides of iron would be fairly 
good materials to use in protective coatings provided 
that they were fully dehydrated and contained no sul¬ 
phur compounds, especially sulphate of calcium, which 
in the presence of moisture is a fairly good conductor 
of electricity and therefore acts as an accelerator of 
corrosion. Theoretically good iron oxide—dehydrated 
and sulphur-free—is seldom seen in practical use, as 
results show. 

Sometimes carbonate of calcium (chalk or whiting) 
is added to oxide-of-iron paint for the purpose of cor¬ 
recting the evil due to the presence of sulphur com¬ 
pounds; but this practice is not to be commended, for 
soluble calcium sulphate will then be formed, and solu¬ 
ble compounds, as we have seen in our list of requisites, 
are bad for a protective coating. The solubles help 
to carry moisture to the surface of the iron, and moisture 
sets up the galvanic action which produces corrosion. 
It will be seen, therefore, that the difficulty in the case 
of iron-oxide paints lies not so much in the inferiority 
of theoretic or perfect oxide of iron itself as in the fact 
that the iron oxides obtainable cannot be relied on as 
free from injurious constituents. 


12 


How to Protect Structural Metal 


Red Lead’s Qualifications 

We now come to consider red lead and to judge it by 
the same standard of requirements which we have 
applied to the other materials. 

In the first place, there is no paint which makes such 
a good, hard, tenacious film as red lead. For this one 
reason alone many painters prefer it, in spite of its color, 
for general painting, even of woodwork, brick, etc. 
Red-lead paint dries to a hard, tough layer and gives 
the best foundation for other painting that has been 
devised. Over it almost any kind of paint can be 
applied. It forms an especially good foundation for 
varnishes, varnish paints, enamel paints and all other 
forms of decorative painting. Over a pure linseed oil 
and red-lead paint there is less tendency to check and 
alligator. The red-lead paint adheres to the metal 
with a tenacity that is remarkable. When attempting 
to clean old metal one often finds the red lead clinging 
so fast that it cannot be removed even with wire brushes. 

In the second place, red lead is unquestionably the 
most practicable inhibitor of corrosion available as a 
constituent of protective coatings. 

In the third place, it is an excellent insulator and is 
practically indispensable for painting metal where 
electric currents are present in unusual quantity. A 
German scientist, writing in the Farben Zeitung, 
says: “Red lead is remarkably impervious to electricity 
of high tension, being fully equal to the best india-rubber 
or gutta-percha, as an insulating material.’* 

In the fourth place, pure red lead mixed with pure 
linseed oil makes a paint which contains no constituents 
soluble in water. It therefore passes our fourth require¬ 
ment with a perfect score. 

As to the fifth requirement, impermeability, red lead 
stands especially high. In order to secure a great degree 
of impermeability each of the paint coats must have a 
reasonable thickness. If the paint is brushed out too 
thin, one or more additional coats must be applied to 
give proper thickness of coating. The working qualities 


How to Protect Structural Metal 


13 


of red lead mixed with linseed oil are such that the 
film spread with it is of a superior character. 

Impermeability is also affected by the amount of 
pigment present in the film. Generally speaking, the 
greater the amount of pigment, the more impermeable 
the paint will be. The increase of the proportion of 
pigment to oil must stop, of course, when the paint 
becomes unworkable. Red lead is noted for the large 
quantity of it which can be mixed with a gallon of lin¬ 
seed oil and still give a good working paint. 

Furthermore, it has been found that the finer the pig¬ 
ment, the more impermeable the paint; but the fineness 
of the pigment must not be increased beyond what 
will permit the presence of the largest quantity of pig¬ 
ment in the paint. Red lead as we make it is an exceed¬ 
ingly fine, uniform pigment and yet makes a splendidly 
working paint at the proportion of four parts pigment 
to one part oil. 

To recapitulate, red lead stands high on the score of 
impermeability because, (a) it produces a good thick 
film, (b) it requires a minimum of vehicle and (c) as 
we make it, it is a fine, uniform pigment. 

The sixth requirement is met perfectly by red lead. 
It has the most distinctive color of any of the pigments 
usually employed as paints for metals. Its bright orange 
hue is readily distinguished from the dark gray or black 
of iron and steel, which makes it an admirable priming 
paint, considered from this point of view. An inspector 
can readily see whether any spots have been left uncov¬ 
ered. The second coat of red lead can be slightly tinted 
with a few ounces of lamp black, thereby rendering it 
distinct from the first coat. On the third coat one may 
return to the natural orange red of the red lead, or deepen 
it still further with lamp black. 

What Red Lead is and How it is Made 

Red lead is an oxide of lead and if of theoretical purity, 
contains 90.65 per cent, of lead. Its formula is Pb 3 0 4 
and apparently it is plumbate of lead, formed by the 


14 


How to Protect Structural Metal 


combination of peroxide of lead (Pb0 2 ) and litharge 
(PbO). It is a red powder varying in color from a light 
orange to a dark red. 

Metallic lead is melted and, in the molten condition, 
is slowly oxidized to litharge. This litharge is a more or 
less yellow substance and, for the purpose of making 
red lead, should be as free from crystals as possible. 
The litharge is finely ground and then placed in a rever¬ 
beratory furnace and subjected to a low red heat. At 
this temperature it slowly absorbs oxygen and is con¬ 
verted into red lead according to the following equation: 
3PbO+0=Pb 3 0 4 . 

The oxidation of litharge to red lead is never complete; 
that is to say, it is almost impossible, in the present state 
of the art, to oxidize all of the litharge to red lead. 

There is one form of red lead, using the term in its 
generic sense, which is made by the oxidation of white 
lead. This is known as orange mineral, and, on account 
of its original fineness and its amorphous condition, is 
more readily oxidized and, consequently, usually con¬ 
tains a lower percentage of litharge than red lead made 
from metallic lead. 

The temperature at which litharge is manufactured is 
ordinarily above 1600° F. The temperature at which 
litharge is converted into red lead is between 900° and 
1000° F. If the temperature is materially below 900°, 
little or no oxidation takes place. If it is materially 
above 1000°, the red lead gives up oxygen and is con¬ 
verted back into litharge. 

Red Lead Should be Fine and Highly Oxidized 

For painting purposes, red lead should be as fine as 
possible. If it is not sufficiently fine, it will tend to run 
when mixed with linseed oil and it will have an inferior 
covering power. Red lead should be oxidized as highly 
as is reasonably possible; that is, it would appear that 
a red lead which contains over 90 per cent, red lead and 
under 10 per cent, litharge makes the best combination 
for painting purposes, and the standard of quality should 
be placed at this figure. 


How to Protect Structural Metal 


15 


The color of red lead depends to some extent upon the 
purity of the pig lead or other materials from which it 
has been made. If made from a reasonably pure pig 
lead it will have a bright, clean color. The difference 
in depth of color depends largely upon its fineness. 
The finer the red lead, generally speaking, the more 
inclined it is to an orange color. The coarser the red 
lead, generally speaking, the deeper will be the red color. 
Red lead, if finely ground and made from unvitrified 
stock, should to the naked eye show only occasional 
glistening particles. 

No Mill Necessary in Mixing 

In the preparation of paint by mixing red lead with 
linseed oil the use of a mill is unnecessary. The red lead 
mixes readily and can be stirred into the oil so as to 
obtain a suitable paint with little difficulty. It has 
some tendency to settle out of the oil, so that the paint 
should be occasionally stirred during its use. 

If the red lead contains a high percentage of litharge, 
this litharge is apt to act on the oil, forming a lead soap 
and, when allowed to stand for any length of time, 
occasions hardening in the bottom of the keg or barrel 
in which it has been mixed. If, however, the red lead 
is finely ground and contains less than 10 per cent, of 
litharge, the tendency to harden is not great; so that the 
paint mixture containing such a red lead can be allowed 
to stand several days without becoming hard enough 
to prevent its being readily blended with the oil again. 

In the preparation of red-lead paint, raw linseed oil 
can be used, or a mixture of raw linseed oil and boiled 
oil in the proportion of two of raw to one of boiled oil. 
It is preferable not to use any liquid drier, as that con¬ 
tains a volatile thinner, such as turpentine, which tends 
to impair the working qualities of the paint. Generally 
speaking, the amount of red lead to be used in the 
preparation of red-lead paint should be as large in 
proportion as possible in order to obtain the best results. 
Thirty-three pounds red lead to one gallon of oil is 


16 


How to Protect Structural Metal 


recommended as a general proportion, although twenty- 
eight pounds to the gallon of oil may be found more 
practical under some conditions. A reduction in the 
amount of pigment should be made only when the 
circumstances of the case particularly demand it. 

Red Lead’s Relation to Linseed Oil 

The nature of the relation between red lead and 
linseed oil in paint is a matter of some dispute. It is 
believed by some that red lead forms a cement by com¬ 
bining with the linseed oil. It would seem, on the other 
hand, that this combination only takes place in pro¬ 
portion to the free litharge present and not between the 
red lead and the linseed oil. 

It appears also that much of the character of red- 
lead paint is given to it by the effect the red lead has 
upon the drying of the oil, the lead and the oil drying 
all the way through, while a manganese drier dries on 
the surface. It has been suggested that the boiled oil 
used with red lead should contain no manganese. This 
may be a good practice. It seems more likely, however, 
that the amount of lead present is sufficient to overcome 
any tendency towards surface drying given to the 
boiled oil when manganese is present in it. 

The Uses of Red Lead 

One might cover the uses of red lead as a protective 
paint for metals in the words: “Wherever metal is 
used.” It may be profitable, however, to enumerate 
some of the more important fields in which a protective 
paint is required and call attention to some of the con¬ 
siderations peculiar to each. 

Structural Iron and Steel 

The architect and engineer are probably more vitally 
interested in the proper paint for metal work than any 
other class of paint users, for more serious consequences 
follow a mistake upon their part. Not only may vast 


How to Protect Structural Metal 


19 


and other steel structures, should persuade gas compa¬ 
nies and water companies to use the same material for 
painting gasometers, stand-pipes, tanks, etc. 

Other paints may be had which will show lower first 
cost, but there is none which will maintain the plant at 
such a small expenditure per year. Red lead is a real 
preservative of iron and steel. 

Metal Roofs 

There is no metal used as roofing, except lead itself, 
which can stand the weather without being painted. 
Tin, galvanized iron or steel should be coated with red 
lead and linseed oil as hereinafter explained in detail. 
The roof need not be left the natural color of the red 
lead if that color is undesirable. If a light tint is wanted, 
white-lead paint tinted to any desired shade is the 
paint for the finishing coats; if a dull red or brown is 
suitable, the last red-lead coat may be toned with lamp 
black. 

Cornices and Other Galvanized Iron Work 

Galvanized iron presents difficulties in painting 
because the coating left on it by the galvanizing process 
seems to repel most paint. Red lead and linseed oil 
paint will stick to it better than any other material. 
Cornices or other parts made of galvanized iron should be 
allowed to weather or be treated with a special solution, 
as described on page 30, before painting. Red lead 
paint should then be applied as to iron. 

Interior Metal Work 

Steam radiators, registers, pipes, grilles, water-tanks 
and every piece of exposed metal work inside of a build¬ 
ing should be painted first with red-lead paint, then 
finished with white lead and linseed oil, tinted to suit 
the color scheme of the room. 


20 How to Protect Structural Metal 

Fire Escapes, Fences, Etc. 

Fire escapes, fences, iron gates, grilles and ornamental 
exterior metal work of all kinds should be painted with 
red lead and linseed oil. 

Red Lead in the Factory 

Besides its use on the structural members of the 
building itself, the contents of a factory frequently 
require red-lead paint. Machinery, trucks, iron pipes, 
tanks, etc., on the interior, and smoke-stacks, stand¬ 
pipes, conveying machinery, derricks, etc., out-of-doors, 
should be painted with pure red lead first and finished 
with red lead toned with lamp black or with whatever 
finishing paint best suits the conditions. 

For Steel Cars 

For steel cars red lead is the ideal paint, not only 
because of its general anti-rust qualities but because 
it makes a hard film which resists* in a superior way the 
friction and hard knocks to which such cars are subjected. 

Painting of Steel Ships and Boats 

Nowhere has red lead proved itself more of a property- 
preserver and money-saver than in the painting of the 
hulls of steel ships and other metal parts of such craft. 
From the United States Government to the maker of 
the smallest craft, vesselmen are constant users of red 
lead in enormous quantities. Whether on salt water 
or the great inland seas, red lead stands out as the great 
ship paint. Many proofs of the truth of this statement 
could be adduced, but none stronger than the fact that 
marine insurance companies practically condemn all 
but red-lead-protected vessels by charging a much 
higher rate for those from which red-lead protection has 
been omitted. 

The hulls, cargo holds, coal bunkers, chain lockers 
and, in fact, all metal parts of ships should be painted 
with red lead as hereinafter described. 


How to Protect Structural Metal 17 

sums of money be lost through the imperfect protection 
of the iron and steel skeletons of their structures, but 
human life itself hangs upon the proper preservation of 
those great steel frames. 

An architect or an engineer may correctly figure the 
stress and strain, and the manufacturer may conscien¬ 
tiously turn out steel of the finest strength and quality, 
but unless rust is kept from the columns, beams and 
girders, the strong, safe skyscraper of to-day may be¬ 
come a death-trap a few years hence. 

An excuse which might pass muster if only ordinary 
business risks were involved is utterly inadequate to 
defend the use of a substitute for red lead. 

Thus one sometimes hears an excuse like-this: “Yes, 
I know red lead is the best paint for metals, but what I 
use is more convenient and I guess it does pretty well.” 

In the face of what is at stake, it is scarcely con¬ 
ceivable that any responsible man could make two 
such admissions in the same breath, namely, that “red 
lead is the best ” but “I am using something else” 

Should Steel Imbedded in Concrete be Painted? 

It is often asked: Is the imbedding of structural iron 
or steel in concrete sufficient to prevent the rusting of 
the metal members, or should the latter be painted 
before they are surrounded by the concrete? 

We have seen in our brief discussion of the nature of 
corrosion and the remedies for it, that alkaline solutions 
tend to change the nature of the iron and render it 
immune to the galvanic influence which produces 
rusting. It would seem, therefore, that the caustic 
lime in the cement should itself be the best possible 
insurance against the decay of the iron imbedded in it. 
As a matter of fact, what we would expect does take 
place and as long as the cement remains caustic the metal 
is perfectly immune to corrosion. The difficulty is, the 
cement does not remain caustic. It absorbs carbonic 
acid from the air and the caustic lime becomes converted 
into insoluble carbonate of lime, which is a poor pre¬ 
venter of corrosion. 


18 


How to Protect Structural Metal 


Protection of the iron by means of the concrete would 
be possible, also, only as long as there is perfect contact 
with the metal. This in practice is very difficult to 
attain or maintain. It is seldom, in the average struc¬ 
ture, that voids or open spaces are not present between 
the iron member and the surrounding concrete. Usually 
the contact is not perfect at the beginning and the 
chemical changes caused by the absorption of carbonic 
acid by the concrete, cause a loosening of the bond 
between the iron and concrete, even where contact at 
first was good. 

Through these spaces moisture-laden air flows and 
even water from leaky roofs, scrubbing brushes, water- 
pipes, drains and steam-pipes seeps down, causing 
corrosion. For the same reasons, the encasing of structural 
iron in shaped brick is inefficient to prevent corrosion. 

If complete imbedding of the iron or steel in a good 
non-porous concrete which can be kept caustic is not 
practicable, the metal members should be painted with 
red lead before encasing them. 

Iron and Steel Bridges 

There is no structure which needs the best possible 
protective paint more than a steel bridge. Whether 
maintained by a railroad or by the people, represented 
by their county commissioners or city department, 
economy of up-keep should be of the utmost interest. 

A paint which gives perfect protection to a metal 
makes a bridge practically permanent, so far as the 
ravages of the weather are concerned. Its use is there¬ 
fore economical, no matter how much cheaper the first 
cost of substitutes may be. Red lead is the only protec¬ 
tive paint which has been shown to be an absolute 
rust preventive. 

Gasometers and Stand Pipes 

The desire for economy which influences great rail¬ 
road corporations to use red lead to protect their bridges 


How to Protect Structural Metal 


23 


In the third test, strips of sheet iron received two coats 
of the same paints used in the first two experiments and 
were immersed in water for three months. The amount 
of rust in each bottle was accurately weighed and cal¬ 
culation was made on the basis of pounds per 1500 
square feet. 

Again red lead was the only paint out of thirty-seven 
to come out with a perfect score. There was absolutely 
no corrosion of those strips protected by red lead. 

Of the other pigments, deep iron oxide allowed 123 
pounds of rust; middle iron oxide, 134 pounds; extra 
bright iron oxide, 137 pounds; pure graphite, 215 
pounds; Indian red (oxide of iron), 227 pounds; ivory 
black (carbon), 250 pounds; turkey red, 262 pounds; 
boiled linseed oil, 500 pounds. 

Ranging between these at various points were various 
pigments and mixtures of pigments. They are of no 
particular interest as no one now seriously recommends 
any of them. It is interesting, however, to observe 
that white lead, zinc oxide and lithopone, which are not 
urged as metal protectives, proved superior to all of 
the so-called protective coatings except red lead. The 
latter was in a class by itself, being the only one to 
protect the iron perfectly. 

Mr. Smith also referred to another test he had made 
two years before in which red lead again was the only 
paint which allowed no corrosion whatever. It was in 
perfect condition after two years. 

A Five Year Service Test 

One of the best field experiments coming to our notice 
was that made by Mr. R. D. O’Keefe, superintendent 
of bridges, Port Huron, Mich. To decide what protec¬ 
tive paint the city should use, Mr. O’Keefe painted 
half of one bridge with our pure red lead and the other 
half with graphite. At the end of five years, the red 
lead was in perfect condition, the graphite was washed 
away and the steel was badly pitted and rusted. All 
the Port Huron bridges are now painted with red lead. 
Here is Mr. O’Keefe’s letter: 


24 How to Protect Structural Metal 

Port Huron, Oct. 18, ’06. 

Sirs: Five years ago I had the lower part of Military Street 
Bridge painted with your pure red lead and linseed oil, and 
the upper part with a graphite paint, for a test, and am pleased 
to inform you that the red lead is in first-class condition and 
has kept the bridge from corroding, while the other paint used 
on the upper part did not give satisfaction as it would not stand 
the acid which comes from the river. We are going to paint all 
the other bridges in the city, and am glad to inform you that 
we will use your red lead and linseed oil for all bridge work. 

Yours respectfully, 

(Signed) R. D. O’Keefe, 

Sup’t of Public Works. 

The Proper Care of Metal Before and After 
Painting 

The application of the right paint is the most vital 
step in the prevention of corrosion, but every other 
possible precaution should be taken. The following 
points should be carefully observed. 

It is exceedingly important to clean off rust before 
painting. Rust is an accelerator of rusting. It is also 
apt to cause the peeling of the paint. 

Have the surface to be painted as smooth as possible. 
It has been observed that brightly polished steel plates 
which have been scratched, corrode slowly except at 
the scratches, where they rust rapidly. Structural steel 
makers may some day realize the importance of this 
phenomenon and provide structural steel with much 
smoother surface than now. At present, structural 
steel is a rough piece of manufacture. Care should 
be exercised at the mill, however, to produce as smooth 
and clean a product as possible. Then the responsibility 
is upon the contractor to keep it so. 

The practice of throwing iron and steel members on 
the ground and allowing them to be covered with dirt 
and refuse cannot be commended. They should be 
handled with care and placed on proper supports. As 
far as possible they should be kept under cover, unless 
they are to be used within a comparatively short time. 

For years the practice of giving structural steel one 
coat of protective paint before it left the shop held 
universal sway. Of late, however, the custom has been 


How to Protect Structural Metal 


21 


The demands made upon the protective coating of 
vessels are most trying. Not only is the hull in the water, 
but there is the friction against docks in the landings, 
the rough usage which the holds receive in the moving 
of freight and, withal, the exposure to varying atmos¬ 
pheric conditions as the vessel sails from place to place. 
It is a significant fact therefore that the standard pro¬ 
tective coating for vessels both in the fresh water of the 
Great Lakes and the salt water of the oceans, is red lead. 
Last coats of other materials are frequently used because 
of their greater adaptability to decorative demands or 
because of power, real or fancied, to prevent fouling of 
bottoms. White lead, either natural or tinted, is nec¬ 
essary for last coats when light tints are desired, and 
lamp black is excellent if black is preferable to the orange 
peculiar to red lead. 

But custom is pretty well agreed upon red-lead for 
the coat which goes next to the iron or steel. The 
reason has already been explained in connection with 
the protection of these metals in other work. There is 
no paint which clings to metals so well as red lead. 

The best proof of the superiority of red lead-paint for 
all metal parts of vessels is its general use for that pur¬ 
pose by the United States Government and an over¬ 
whelming majority of vessel owners both on the seaboard 
and on the Great Lakes. 

It is an interesting practice among owners of great 
freighters, especially on the Great Lakes, to mix white 
lead and red lead for the finishing coats in the holds. 
This is done to secure the wearing quality of red lead and 
at the same time the light tint which the white pigment 
contributes, thus making the dark hold lighter. 

How Much Red Lead to the Gallon? 

The practice of various architects, engineers, vessel 
builders and owners, painters, etc., in regard to the 
formulas used in mixing red-lead paint varies. The 
United States Navy Department has general specifica¬ 
tions which allow about thirty-one pounds of red lead 


22 How to Protect Structural Metal 

to the gallon of linseed oil. From this the formulas run 
both ways, up to thirty-three pounds to the gallon and 
down to twenty-five pounds to the gallon. Good results 
are had by all, but it has been seen that one of the great 
desiderata in a protective paint is richness in pigment 
as compared to oil. Therefore, it is evident that those 
who take full advantage of red lead’s power to mix well 
with a small quantity of oil are securing the greatest 
benefit. Only exceptional conditions really justify the 
risk of the smaller proportions of pigment sometimes 
used. We recommend not less than twenty-eight 
pounds of red lead to the gallon and we consider thirty- 
three pounds to the gallon as the best for all general 
purposes. 


Laboratory and Field Tests 

Among the most conclusive laboratory experiments 
for the purpose of testing protective paints is that 
reported in the Journal of the Society of Chemical 
Industry of December 30, 1899, page 1093. It is con¬ 
tained in an address on “Protective Paints for Iron” 
by Harry Smith, F. I. C., before the Newcastle Section 
of the Society of Chemical Industry at the Durham 
College of Science, England. 

Perfectly Protected by Red Lead 

Three tests were made: (1) Shallow iron dishes were 
painted with the various paints and filled with water, 
which was allowed to evaporate. As fast as the water 
evaporated the dish was refilled. During the three 
months of this severe test rust was formed on all the 
dishes except those protected by red lead. Those dishes 
protected by linseed oil alone were the first to corrode 
and produced the greatest quantity of rust. 

In the second test painted plates were exposed to the 
weather for twelve months. This was a mild test and, 
with the exception of those coated with oil alone, no 
great deterioration was observed on any of the plates. 


How to Protect Structural Metal 


27 


and steel structural work. Of course, most of them are 
using more or less of other materials all the time in a 
spirit of investigation. Cheaper paints are being offered 
continually and the desire for economy dictates that 
thorough tests shall be made wherever there is reasonable 
promise of obtaining good results for less money. It 
is the more remarkable, therefore, that an admittedly 
high-priced material holds its own against all comers. 

The Railroad Companies 

The New York Central and Hudson River Railroad 
Company uses red lead exclusively where no chances 
are to be taken. Its engineers, under direction of Mr. 
Noel C. Carpenter, engineer in charge of structures, 
have made very extensive tests in recent years to deter¬ 
mine the relative merits of various materials and have 
come to the conclusion that nothing is so good for a 
protective coating as red lead. Consequently, shop 
coats—the protective paint—on all important structural 
iron and steel work, whether for bridge or buildings, 
are red lead. Finishing coats vary according to condi¬ 
tions to be met. 

Most of the other large railroads also use red lead for 
protective coatings. 

The Federal Government 

The United States Government is a big user of red 
lead. The Navy Department uses tons annually, while 
on public buildings of all kinds red lead is specified for 
the protection of the structural metal work. At the 
Brooklyn Navy Yard, where a great deal of repairing 
of ships is done, an officer said: “We find that if a ship 
has once been painted well with red lead, little is required 
thereafter but to touch up abrasions in the outer coat. 
The protective coats of red lead are generally found 
intact.” 

Great Lake Fleets 

The United States Steel Corporation maintains an 
immense fleet of big freight ships on the great lakes 


28 


How to Protect Structural Metal 


for carrying ore and other material. After exhaustive 
experiments this great corporation has abandoned all 
other protective paints and is using red lead exclusively. 
The general superintendent of a company which builds 
many of the steel corporation’s ships says in an auto¬ 
graph letter in our possession: “I consider a thorough 
application of red lead upon a properly cleaned steel 
ship (all crevices or indentations that may be caused by 
pitting or rust being filled in) to be absolutely the best 
preservative that can be used.” 

City of New York 

The City of New York, whose annual bill for building 
and maintaining public structures of many kinds is 
greater than that of many states and some kingdoms, 
is an important consumer of red lead. Among the recent 
structures which are attracting public attention are the 
Queensboro Bridge over the East River at Blackwell’s 
Island (cantilever type), and the new Manhattan Bridge 
(suspension type). These, as well as the older structures, 
Brooklyn Bridge and Williamsburg Bridge, are pro¬ 
tected by our red lead. 

As to Quality in Red Lead 

Red lead is not all alike. Some manufacturers, 
relying upon the excellence of oxide of lead in a general 
way, do not pay much attention to making their red 
lead uniform in composition, texture, color, etc. This 
fact has led many large users of red lead to adopt certain 
specifications on these points to which they require the 
material to measure up. 

The requirements of the United States Government, 
Navy Department, are as follows: 

“The dry pigment must be of the best quality, free 
from all adulterants, and contain at least 94 per cent, 
of true red lead (Pb 3 0 4 )—equivalent to 32.8 per cent, of 
lead peroxide (Pb 2 0)—, the balance to be practically 
pure lead monoxide (PbO.) It must contain less than 
0.1 per cent, of metallic lead, and be of such fineness 


How to Protect Structural Metal 


25 


questioned and many architects and engineers are 
having the steel delivered unpainted. The new idea has 
much to recommend it—two considerations especially. 
The first is, that a certain amount of weathering is 
desirable to rid the iron of mill scale. The other is, that 
shop coats are generally poorly done by cheap labor 
and really do more harm than good, because they cover 
up the evidence of poor work in the matter of cleaning 
the metal. In case there is no shop coat, the first painting 
should be done just before assembling begins. 

Scale and all other foreign material must be removed 
before painting. The relative value of the sand-blast, 
wire-brush and pickling, as methods for cleaning, are 
discussed elsewhere in this booklet. 

Little can be done on a structure toward securing 
equality of surface conditions—that is, the same com¬ 
position of metal—but what can be done should be 
done, and where palpably different conditions exist, 
such as where wrought iron rivets and bolts are used on 
Bessemer steel members, extra precaution should be 
taken with the painting at such points. 

No paint is absolutely impermeable to water or to 
gases. It is therefore worth while to keep the moisture 
contents of the air as low as possible. This has particu¬ 
lar reference to subways, cellars, etc. In exposed struc¬ 
tural work, all gutters or pockets in which rain-water 
might otherwise collect should be made to drain as 
nearly dry as possible. In subways and viaducts car¬ 
bonic and other acids are apt to collect. This should be 
prevented as far as practicable by mechanical or chemi¬ 
cal means. 

It is very important to protect bridges and viaducts 
against the salt drippings from refrigerator cars, for the 
saline solutions are very apt to accelerate corrosion. The 
same caution should be observed in all other places where 
salt water is apt to come in contact with painted metal. 

Preparing for Painting 

Just before assembling begins all parts of the metal 
which are not to be exposed—that is, those parts which 


26 


How to Protect Structural Metal 


cannot be cleaned and painted after erection—should 
be thoroughly cleaned with wire brushes and scrapers 
and at least two coats of red lead should be applied to 
these surfaces. 

While the use of the sand blast is theoretically a 
desirable thing, so few contractors are equipped or are 
willing to use it that the utmost that can be done at 
present is to insist upon thorough cleaning with wire 
brushes and scrapers, with the assistance perhaps of 
the hammer and cold chisel. This cleaning should be 
done under the proper supervision of a competent 
inspector. Painting should immediately follow cleaning. 

The selection of proper men to do the cleaning is a 
matter of no small importance. These men should be 
impressed with the importance of their work, which 
should be specialized as far as practicable. The habit of 
contracting for cleaning and painting work together 
and placing the whole in the hands of the employers of 
unskilled labor is a cause of much bad work. As far as 
practicable , the cleaning should be done separately by men 
whose direct interest is that of the owner. 

For the cleaning of small articles, pickling in sulphuric 
acid is an excellent method, care to be taken afterwards 
to wash the sulphuric acid all off the iron and then to 
cover the articles with caustic lime until ready to paint. 
The following method of treatment should give satis¬ 
factory results: Dip the articles, if at all greasy, in a 
hot ten-per-cent, caustic soda solution; then in hot 
water; then for, say, ten minutes in hot ten-per-cent, 
sulphuric acid; then in hot water; then in hot ten-per¬ 
cent carbonate of soda (soda ash) solution; rinse well 
in hot water, and pack in slacked lime until time for 
painting has come. Remove from the lime; wash well 
with water; brush clean, and dry rapidly. The articles 
when dry will be ready to paint. 

Prominent Users of Red Lead 

The railroads of the United States are practically a 
unit on the use of red lead for the protection of iron 


How to Protect Structural Metal 


31 


seed oil (Formulas 1 and 2) and two finishing coats. 
The finishing coats may be of any color desired, and 
material should be chosen according to circumstances. 
(See “Finishing Paints,” page 31.) 

The first finishing coat should be put on somewhat 
flat or dead, while the final coat should have a full gloss. 
Care should be especially observed in the proper paint¬ 
ing of inaccessible parts before erection. 

Subways. —In the painting of iron and steel in sub¬ 
ways the same general rule should be observed as for 
bridges and viaducts (paragraph preceding), except 
that the bases of all columns and vertical supports 
should have five coats of paint. The first two coats 
should be red lead in linseed oil (Formulas 1 and 2). 
The finishing coats may be as described above for 
“Structural Iron Work for Buildings,” except where a 
white finish is desired. In such cases the third coat 
should be of white lead in linseed oil mixed according to 
Formula No. 9. The fourth coat should be white lead 
in linseed oil mixed according to Formula No. 10. 

If an enamel finish is desired on top of this fourth 
coat, finish with Formula No. 11. 

The bases of columns and vertical supports, for which 
we have advised a fifth coat, should receive three coats 
of red lead in linseed oil, the first and third being mixed 
according to Formula No. 1, the second coat according 
to Formula No. 2 and the fourth and fifth coats accord¬ 
ing to the finish desired. (See “Finishing Paints,” 
page 31.) 

Decorative Iron Work. —Railings, grilles, fences, 
fire-escapes and similar metal work should be painted 
the same as bridges, viaducts and elevated roads. The 
finishing paint will depend largely on the decorative 
demands. The first finishing coat should be applied 
somewhat flat and the final coat with full gloss. Black, 
dark olive and dark brown are serviceable for finishing 
coats. Black may be obtained with lamp black, dark 
olive by using Formula No. 6, and dark brown by using 
Formula No. 7. 

Tin Roofs and Tin Side-Sheathing. —The founda- 


32 


How to Protect Structural Metal 


tion for a tin roof should be very tight, for the rusting 
of such roofs usually begins underneath , not on top. It 
would be good practice to lay tin roofing on building 
paper. Every piece of tin should have one coat of red 
lead (Formula No. 1) on its under side before being 
laid. 

After thoroughly cleaning to remove the rosin and 
fluxing materials, the completed roof should receive 
two coats of protective paint. (Formulas Nos. 1 and 3.) 
The finishing coat may be a red lead paint with from 
four to sixteen ounces of lamp black to the gallon (see 
Formulas Nos. 4 and 7), or any good paint which will 
give the tint desired. Formula No. 7 gives a rich brown 
and is very desirable, but in specifying be careful that 
an iron-oxide paint is not substituted. The latter will 
imitate the red-lead and lamp-black paint very closely 
in appearance but is not so durable. 

Painting Galvanized Iron. —Galvanized iron is 
sheet iron coated with zinc by dipping or by means of 
galvanic or electric action. The process was invented 
and is used in an attempt to protect the iron from 
corrosion. The method is unsatisfactory alone, how¬ 
ever, and it is found necessary to paint galvanized iron 
the same as any other form of the metal. 

Its greatest advantage is the fact that it can be soldered 
and can therefore be used for cornices. Its great dis¬ 
advantage is that, while it requires painting, it resists 
paint. Unless very carefully done the best paint will 
peel from it. 

Where practicable it is a good plan to let the gal¬ 
vanized iron weather until it has developed a tooth, 
then clean the surface with a wire brush. This is fre¬ 
quently impracticable, however, and the following 
method of preparing the surface is recommended by a 
great many excellent painters, although our own experi¬ 
ments with it have not been so uniformly successful as 
to justify a sweeping endorsement: 

In one gallon of soft water dissolve two ounces each 
of copper chloride, copper nitrate and sal ammoniac, 
then add two ounces of crude hydrochloric acid. This 


How to Protect Structural Metal 


29 


that not more than 0.5 per cent, remains after washing 
with water through a No. 21 silk bolting cloth sieve. 
It must be of good bright color and be equal to the 
standard sample in freedom from vitrified particles and 
in other respects.” 

The American Bridge Company states its requirements 
as follows: “This red lead must be strictly pure and 
shall contain at least 80 per cent, of true red lead of 
the composition Pb 3 0 4 ; the total amount of lead 
present shall not be less than 89 per cent., of which not 
more than one-tenth of one per cent, shall be present 
as metallic lead. The color shall be a clean and pure 
tint. The red lead shall be of the fineness that when 
washed with water through a No. 19 silk bolting cloth, 
not more than one per cent, shall be left on the screen.” 

The City of New York in its specifications for the new 
Queensboro Bridge specified as follows: “The red lead 
must be strictly pure and shall contain at least 90 per 
cent, of pure red lead of the composition Pb 3 0 4 ; the 
total amount of lead present shall not be less than 89 
per cent., of which not more than one-tenth of one per 
cent, shall be present as metallic lead. The color shall 
be a clean and pure tint. The red lead shall be of the 
fineness that when washed with water through a No. 
19 silk bolting cloth, not more than one per cent, shall 
be left on the screen.” 

Our red lead easily fulfils these strict requirements, 
which accounts for its general use by all large and 
discriminating consumers. We welcome all such tests 
on the part of buyers and willingly co-operate to obtain 
the best results possible in the painting of structural 
steel. 


Mixing and Applying the Paint 

General Cautions. —Where parts of iron and steel 
are unusually exposed to corroding or abrasive influences, 
they should receive extra attention in the matter of 
painting and preferably an extra coat should be applied 
to all such places. Thus all bolts, rivet-heads, all 


30 


How to Protect Structural Metal 


edges and all comers, should have an extra coat of 
protective paint so that at these points the paint may be 
thicker than where the surface is simply flat and there¬ 
fore not subject to especially destructive influences. 

All parts in contact should be flushed fully with paint 
as it is at such points that corrosion is apt to be espe¬ 
cially insidious. Engineering construction should pro¬ 
vide for the accessibility of all parts for the purpose of 
painting. 

In all cases the application of the paint should be 
done by competent workmen, using round brushes 
wherever practicable. The round, pound bmsh is an 
excellent type of bmsh to use. 

The paint should be of such thickness as to require 
a strong arm and wrist to bmsh it out. 

Structural Iron Work for Buildings. —In build¬ 
ings, stmctural iron and steel are generally encased in 
brick or concrete. We have already called attention 
on page 15 to the advisability of painting stmctural 
iron and steel which is so encased. All such stmctural 
metal work should receive three coats of red lead paint, 
and in addition, such touching up of edges and rivet- 
heads and bolts as may be necessary to thoroughly 
protect these especially exposed parts. The first coat 
should be of pure red lead and linseed oil (Formula No.l). 
The second coat should be red lead and linseed oil with 
an ounce of lamp black in oil added for the purpose 
of changing the tint. (Formula No. 2.) The third or 
finishing coat may be a darker red-lead coat, (Formula 
No. 4), a dark olive (Formula No. 6) or it may be a 
black coat of finely ground graphite or lamp black 
(Formula No. 5). The addition of a small percentage 
of varnish to this finishing coat will improve its 
quality. 

Bridges, Viaducts and Elevated Roads. —Stmc¬ 
tural iron and steel exposed as it is on bridges, viaducts, 
elevated roads and all similar stmctures should receive 
the same treatment as described above for iron work 
except that they should have four coats instead of three, 
consisting of two protective coats of red lead and lin- 


How to Protect Structural Metal 


33 


must be done in an earthen or glass vessel, never in tin 
or other metal receptacle. Apply the solution with a 
wide, flat brush. 

Steel Ships. —The bottoms of steel vessels, cargo 
holds, coal bunkers, chain lockers, and in fact all metal 
parts of vessels, should first be freed from dirt and rust 
and then be treated with a coat of red-lead paint, mixed 
according to Formula No. 1. This should be followed, 
when dry, with a coat of red lead paint to which an ounce 
of lamp black and oil has been added. (Formula No. 2.) 
A third coat of pure red lead and oil mixed according to 
Formula No. 1 should be next applied, unless for any 
reason a dark shade is desired, in which case any of the 
finishing paints, recommended under that heading below, 
may be used. 

The interiors of cargo holds and other metal parts of 
ships should be treated the same as bottoms except 
that in many cases finishing coats of either lighter or 
darker hue are desired. The finishing coats spoken of 
above are available for these purposes. There is another 
popular treatment now being practiced for the sake of 
lighting up what would otherwise be a dark place. This 
is to apply over the red lead coats a coat of red lead 
mixed with white lead in the proportions of two parts 
red lead to one of white lead. (See Formula No. 12.) 
A large number of steamship companies, especially on 
the great lakes, are using this formula. 

Finishing Paints 

When iron and steel have had a sufficient number of 
coats of good protective paint, the problem is to select 
suitable finishing paints. Generally speaking, any good 
paint can be applied over a suitable foundation. By 
good paints we mean paints that, selected as to color 
for artistic reasons, are reasonably impermeable and 
contain no actually deleterious constituents. If the 
paint is to be exposed out of doors, more care should be 
exercised in the selection of the paint to be used than 
if the paint is not to be exposed. 


34 


How to Protect Structural Metal 


It can be considered good practice to have the finishing 
coat of a color close to that of the original iron: that 
is, if the two or more protective coats start as red, one 
or two finishing coats of black paint on top of this 
would ensure fairly complete protection and covering 
of the metal. The black paint could not be applied 
imperfectly without such imperfect application becom¬ 
ing immediately noticed by the showing through of the 
red protective coatings. 

Where the iron and steel are exposed, the kind of 
finishing paint to use depends upon the color desired. 

For railroad bridges and structures similarly exposed, 
a black paint is to be preferred. For decorative purposes, 
it is often desirable to use a dark olive. For interior 
work, enamel paints are sometimes used; in which case, 
white lead or zinc enamels are to be preferred to those 
made from lithopone. 

A small amount of varnish is sometimes used also in 
other finishing paints besides enamels. There is no 
objection to this, as it adds hardness and impermeability 
to the coat. When such paints begin to decay, however, 
they are apt to decay with great rapidity and conse¬ 
quently should be watched carefully. 

In certain places, such as train sheds, where the 
color is not important, it has been difficult to obtain 
satisfactory protection on account of the sulphur in the 
engine smoke; and in such cases the best protection 
on record has been obtained by applying, over the wet 
paint, sheets of thin paraffin paper, subsequently giving 
this also a coat of paint. 

There are so many conditions which determine the 
kind of paint to be used as a finishing paint that we can 
simply conclude this phase of the subject by repeating 
that, when a good foundation paint has been applied 
to iron and steel, any good paint can be used over it 
as a finishing paint. 

Tints for Finishing Coats 

In cases where decoration is important and especially 
where the painted iron work should be brought into 


How to Protect Structural Metal 


35 


harmony with the surrounding color scheme, it is very 
often desirable to use white or light tints. In all such 
cases pure white lead and linseed oil is the finishing 
paint to use. These materials make the most durable 
finishing paint for average conditions and by using 
with them the proper tinting colors, any desired tint 
or shade can be obtained. 

White lead and linseed oil are especially adapted for 
use over red lead and linseed oil, because linseed oil 
dries much the same with these two pigments and there¬ 
fore the two paints make a homogeneous film, as regards 
the dried-oil component. 

A word of caution should be given upon the use of 
red lead and lamp black to form a brown. (Formula 
No. 7.) This gives a color which can be very easily 
imitated by the brown oxides of iron and care should be 
exercised that the latter is not substituted for the 
more durable red lead. 

(Formulas referred to will be found on pages 34 and 35. Form 
of specification in order to secure the highest quality of red lead 
is given on the inside of the back cover.) 



36 


How to Protect Structural Metal 


Mixing and Applying the Paint 

FORMULAS 

Priming and Body Coats 

No. 1.—PURE RED LEAD PRIMING COAT. 

1 gallon linseed oil; (y boiled oil, % raw; or all 
raw oil with y pint turpentine drier added.) 
33 pounds pure red lead. 

No. 2.—RED LEAD COAT, TINTED. 

1 gallon linseed oil; (y boiled oil, y raw; or all 
raw oil with y 2 pint turpentine drier added.) 
33 pounds pure red lead. 

1 ounce lamp black in oil. 

No. 3.—RED LEAD COAT, TINTED. 

1 gallon linseed oil; (y boiled oil, y raw; or all 
raw oil with y pint turpentine drier added.) 

33 pounds pure red lead; 

2 ounces lamp black in oil. 


Finishing Coats 

No. 4.—RED LEAD COAT, TINTED. 

1 gallon linseed oil; (y boiled oil, % raw; or all 
raw oil with y 2 pint turpentine drier added.) 

33 pounds pure red lead; 

4 ounces lamp black. 

No. 5.—BLACK COAT. 

A good black paint of finely ground graphite or lamp 
black with a small percentage of varnish added. 

No. 6.—DARK OLIVE. 

100 pounds pure white lead; 

16 pounds French ochre; 

46 pounds medium chrome yellow; 

19 pounds lamp black in oil. 

(This gives the properly tinted pigment. Linseed oil and 
drier must be added in sufficient quantities to bring it to paint¬ 
ing consistency.) 

No. 7.—DARK BROWN. 

1 gallon linseed oil; boiled oil, % raw; or all 
raw oil with y 2 pint turpentine drier added). 
27 pounds pure red lead; 

1 pound lamp black in oil. 


How to Protect Structural Metal 


37 


No. 8.—WHITE GLOSS FINISH FOR EXTERIOR. 

3H.to 4^ gallons raw linseed oil; 

1 pint pure turpentine; 

1 pint pure turpentine drier. 

100 pounds pure white lead. 

No. 9.—WHITE GLOSS FINISH FOR EXTERIOR. 

(Slightly flatter than No. 8.) 

2K gallons linseed oil; boiled oil, % raw oil 
or all raw linseed oil with y 2 pint turpentine 
drier added.) 

1 gallon turpentine; 

100 pounds pure white lead in oil. 

No. 10.—WHITE FLAT FINISH FOR INTERIOR. 

M gallon raw linseed oil; 

1 % to 2 gallons pure turpentine; 

1 pint pure turpentine drier; 

100 pounds pure white lead. 

No. 11—WHITE ENAMEL FINISH FOR INTERIOR. 
1 gallon light enamel varnish; 

3 pounds pure white lead. 

(Break up the white lead first with a little turpentine to a 
thick paste, then mix well with the varnish.) 

No. 12.—SHIP HOLD FINISH. 

1 gallon linseed oil; boiled oil, % raw; or all 
, raw oil with ^ pint turpentine drier added.) 

22 pounds pure red lead; 

11 pounds pure white lead. 

Note —The formulas for white finishes can be adapted to 
any tint desired by putting in the proper tinting material and 
adding thinners equal to one-half the weight of the tinting 
material. 

Note —When red lead is mentioned in these formulas, dry 
red lead is meant. On the contrary, when white lead is men¬ 
tioned, white lead-in-oil, as usually furnished to the trade, is 
meant. 



INDEX 


A 

Alkalies in paint. 5 

Alkaline solutions for preserving iron. 5 

Architects’ special interest in painting metal work . 14 

Asphaltum. 9 

Available paints . 8 

B 

Black finishing coat.32, 34 

Boats, Steel.18 

Bolts.23 

Bridges, Painting of.16, 26, 28 

Bridges, viaducts and elevated roads.28 

Brown for finishing coat.33, 34 

Bunkers, Coal .18, 31 

C 

Carbon and graphite . 9 

Carbonate of calcium. 9 

Carbonic acid .15, 23 

Care of steel before and after painting.22, 23 

Cars, Refrigerator.23 

Cars, Steel.18 

Caustic lime.15 

Cellars.23 

Cement.15 

Cement* Does Red Lead form a.... .14 

Checking of paint, Causes of. 6 

Chemical analysis of Red Lead. 11 

Chromic acid solutions. 5 

Color in protective paint important.7, 9 

Concrete for protecting iron.15,16 

Concrete, Steel imbedded in. 15 

Cornices and other galvanized iron work.17 






























INDEX—Continued 


Corroding tendency of various metals. 3 

Corrosion, Causes of. 4 

Corrosion, Red Lead as inhibitor of.10 

Corrosion, Relative standing of metals in resisting . 4 

Cracking of paint, Causes of. 6 

D 

Decay in iron and steel. 4 

Decorative iron work.29 

Derricks.18 

E 

Electric action, Rust is. 5 

Electric currents.7, 10 

Electricity, Protective paint must be non-conductor 

of. 6 

Elevated roads .28 

Enamels.32, 35 

Engineers’ special interest in metal paints .... 14 

F 

Factory equipment.18 

Fatigue in steel. 4 

Fences .18, 29 

Field and laboratory tests.20 

Fineness of Red Lead.11, 12 

Finishing Paints.6, 31, 34 

Fire escapes.18, 29 

Formulas (paint) for all protective purposes . . 34, 35 

G 

Galvanized iron, Painting.30 

Gasometers and stand-pipes.16 

Gates.18 

General qualifications of paint. 6 

Getting ready to paint.24 

Good paint for metal, general requirements . . . . 6, 7 

Graphite and carbon . 9 

Grilles.17, 18, 29 

Gutters.23 

ii 





























INDEX—Continued 

H 

Holds, Cargo.18, 31 

How much Red Lead to the gallon.19 

Hulls, ships. 18 

I 

Impermeability of Red Lead.10 

Inhibitor of corrosion, Red Lead as.10 

Insulator, Red Lead as.10 

Insurance rates.18 

Interior metal work.17 

Iron oxides .9,21,30 

Iron—why painted. 5 

Iron and steel bridges.16 

Iron and steel decay . 4 

L 

Laboratory and field tests.20 

Linseed oil—alone and with a pigment . 8 

Linseed oil—effect on Red Lead.14 

Litharge.12, 14 

Lithopone.21 

Lockers.18,31 

M 

Machinery.18 

Manganese, as a drier.14 

Metals, Good paint for. 6 

Metals—relative standing in resisting corrosion . . 4 

Metals—tendency to corrode. 3 

Metal roofs.17 

Metal surface—preparing it to be painted .... 22 

Metal work, Interior .17 

Mineral oils . 8 

Mineral, Orange.12 

Mixing and applying the paint (Formulas) .... 34 

Mixing and applying paint, General cautions for . . 27 

Mixing Red Lead and linseed oil.13 

iii 





























INDEX—Continued 


N 

Nitric acid. 5 

Non-conductor of electricity, Protective paint as . 6 

O 

Olive, dark, finishing coat.29, 34 

Orange mineral.12 

Ornamental metal work.18 

Oxidation of iron and steel. 4 

Oxide of iron.9, 21, 30 

P 

Paints, Protective and finishing. 7 

Paint, protective, Qualifications of. 6 

Pickling.24 

Pipes.17, 18 

Preparing for painting. 22, 23, 24 

Priming-coat formulas.34 

Protective paints.6, 7 

Q 

Quality in Red Lead .26 

R 

Radiators and registers.17 

Railings.29 

Railroad companies as users of Red Lead.25 

Red Lead, Advantage of fineness in.12 

“ “ as a factory paint.18 

“ “ as inhibitor of corrosion.10 

“ “ Distinctive color of.11 

“ “ Fineness and uniformity in.11 

“ “ for general painting.10 

“ “ —how it is made.12 

“ “ Impermeability of.10 

“ “ Mixing linseed oil and.13 

Lead’s qualifications as a paint for metals . . 10 

“ relation to linseed oil.14 

“ requirements of large consumers ... 27 


iv 
































INDEX—Continued 


Red Lead, Tenacity of. 10 

“ Users of.!! 25,26 

Varying color of . 13 

—what it is .U 

—where it is used. 14 

Requisites of a good metal paint. 6 

Rivets, Wrought-iron.23 

Roofs, Tin.17 29 

Rust, Methods of preventing. 5 

Rusting an electric action. 5 

Rusting, Causes of . 4 

S 

Saline solutions.23 

Sand-blast.24 

Ship-hold finish formula. 35 

Shop-coats.23, 25 

Side sheathings, Tin .29 

Sky-scrapers. 15 

Specifications of U. S. Navy for Red Lead paint . . 19 

Stand-pipes.17, 18 

Steel, Advantages of smooth surface on. 22 

Steel bridges, Painting.16 

Steel, Care of.23 

Steel cars. 18 

Steel, Finishing paints for.31 

Steel imbedded in concrete.15 

Steel preservation, Importance of.15 

Steel ships and boats.18, 26, 31 

Structural iron and steel.14 

Structural iron work for buildings.28 

Subways.23, 29 

Sulphuric acid.24 

T 

Tanks.17, 18 

Tenacity of Red Lead.10 

Theory of corrosion. 5 

Tin roofs and tin side sheathings.29 

Tinted coat formulas. 34 





































INDEX—Continued 


Tints for finishing coats.32 

Tints, Making of.33 

Train sheds.32 

Trucks .18 

Turpentine.13 

U 

Uses of Red Lead.14 

Users of Red Lead.25, 26 

Uniformity in Red Lead.11 

U. S. Government large users of Red Lead on vessels 19 
U. S. Navy Department specifications.19 

y 

Varnish.32 

Varying color of Red Lead.13 

Vessels, Red Lead on.18, 19, 25, 31 

Viaducts.28 

W 

What constitutes a good paint. 6 

White flat finish for interior work (Formula) ... 35 

White gloss finish for exterior exposure (Formula) . 35 

Wire brush .24 

Z 

Zinc oxide.21 


vi 



















LIBRARY OF CONGRESS 




















































When specifying paint for metals 
name 


“SOUTHERN 

Pure Red Lead 
and pure linseed oil” 

or 


“NATIONAL LEAD CO'S 
Pure Red Lead 
and pure linseed oil” 











LIBRARY OF CONGRESS 



0 033 266 774 S 


« 





















